1. Field of the Invention
The present invention relates generally to a rolling mill for rolling metals etc, and more particularly to a strip thickness control apparatus for a rolling mill that restrains fluctuations in strip thickness due to an eccentricity of a rolling roll (which will hereinafter simply termed a roll eccentricity).
2. Related Background Art
The roll eccentricity is one of factors that cause disturbances in controlling a strip thickness when rolling the metal etc. Major factors causing the roll eccentricity are:
(1) an influence of a bearing key of a backup roll,
(2) a deviation of an axial core of the backup roll, and
(3) incomplete roundness of a work roll.
If a rolling velocity is fixed, a strip thickness on the delivery side is periodically fluctuated.
There are proposed a variety of control methods of reducing the influence of this roll eccentricity upon the strip thickness. A typical method thereof is that a rolling force is detected as a function of an angle of rotation of the roll, a roll eccentricity is obtained based on this detected value, and a roll gap controller is operated so as to cancel this roll eccentricity. This method must involve so-called kiss-roll in order to detect the rolling force, wherein the upper and lower rolls are brought into contact with each other while being rotated in a state of having no strip.
The kiss-roll is not, however, easy to perform in such a type of rolling mills that consecutive rolling operations are carried out as in tandem rolling, and it is therefore difficult to apply the prior art method described above. Further, as the rolling advance, a state of the roll changes, and a quantity of the roll eccentricity varies. The conventional method is, however, incapable of corresponding to these changes.
It is a primary object of the present invention, which was devised to obviate the problems inherent in the prior art, to provide a strip thickness control apparatus for a rolling mill that is capable of reducing an influence of a roll eccentricity upon a strip thickness even in the rolling mill incapable of easily performing the kiss-roll, and of corresponding to a change in the roll eccentricity as the rolling advances.
To accomplish this object, a strip thickness control apparatus for a rolling mill comprises a strip thickness gauge, provided on a delivery side of the rolling mill, for measuring a thickness of a strip, a moving distance calculating module for calculating a moving distance of the strip from the rolling mill, a rolling roll angle-of-rotation calculating module for calculating an angle of rotation of the rolling roll, a strip thickness deviation calculating module for calculating a deviation of the strip thickness from a target value of the measured value of the strip thickness by the strip thickness gauge, a strip thickness deviation storage module for storing the strip thickness deviation by adding it for every angle of rotation of the rolling roll, a strip thickness deviation input determining module for determining an input timing for inputting the strip thickness deviation to the strip thickness deviation storage module on the basis of the moving distance of the strip and the angle of rotation of the rolling roll, a strip thickness deviation output determining module for determining an output timing for outputting the strip thickness deviation stored in the strip thickness deviation storage module on the basis of the angle of rotation of the rolling roll, and a manipulated variable calculating module for fetching the strip thickness deviation stored in the strip thickness deviation storage module at the output timing determined by the strip thickness deviation output determining module, and determining a manipulated variable of a roll gap controller of the rolling mill, which eliminates the strip thickness deviation.